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Old 27-07-2018, 06:59   #1
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Can windgen mess up Amp-hr count?

My charing system consists of both wind and solar, each on separate controllers. I have a Victron battery monitor (BMV 602). The solar is on a 3-stage MPPT Victron controller. The wind is on a basic voltage regulated controller. Just cuts off at a certain voltage.

In the morning we are usually down anywhere from 30 to 70 amp-hrs based on the hour counter on the BMV. But what often happens is that it will get down to around -20 amp-hrs, and then it will suddenly leap to zero.

Why?

I assume the BMV can accurately measure amps-out and amps-in. Why does it commonly jump to the zero mark like this?

My speculation is that the highly variable input from the windgen is somehow not fully being accounted for, but I really don’t know.

BTW, I don’t actually believe my batteries are back to 100% when the counter reaches zero — at least not based on the behaviour of my MPPT which usually reaches float some time after the BMV reads 100%.
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Old 27-07-2018, 07:07   #2
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Re: Can windgen mess up Amp-hr count?

My Link-2000R monitor will gradually drift away from an accurate Ah reading, and then during charging will reset the Ah counter to zero when the battery voltage and charging current meet the programmed "fully charged" parameters. Perhaps your monitor uses a similar algorithm?
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Old 27-07-2018, 07:43   #3
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Re: Can windgen mess up Amp-hr count?

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My Link-2000R monitor will gradually drift away from an accurate Ah reading, and then during charging will reset the Ah counter to zero when the battery voltage and charging current meet the programmed "fully charged" parameters. Perhaps your monitor uses a similar algorithm?
Good thought Paul. Iíll have to dig out the manual. I havenít reset the monitorís settings for some time.

ButÖ I assume the amps-in/amps-out is a direct measure independent of the manually programmed data. I have little faith in the SOC percentage, but shouldnít the meter be able to measure amps in/out directly?
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Old 27-07-2018, 07:45   #4
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Re: Can windgen mess up Amp-hr count?

I'm thinking it auto restes also, and these auto resets can lead you down a bad path, just like the chargers that trip to float automatically, they all seem to do so prematurely.
However if your wind Genny bypasses the shunt and goes directly to the battery bank ,that can confuse things as the amp hour counter won't see the charge
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Old 27-07-2018, 08:05   #5
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Re: Can windgen mess up Amp-hr count?

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Good thought Paul. I’ll have to dig out the manual. I haven’t reset the monitor’s settings for some time.

But… I assume the amps-in/amps-out is a direct measure independent of the manually programmed data. I have little faith in the SOC percentage, but shouldn’t the meter be able to measure amps in/out directly?
The amps in vs amps out calculations use a programmable Peukert's Law exponent to make corrections in the totalized number. My Link 2000R uses a programmable "Charge Efficiency Factor" as well. If these don't exactly match the characteristics of your battery (which changes over time and usage and probably other parameters) then the Ah error will accumulate. This is why the controller does the automatic Ah reset when the "charged" parameters are met -- to avoid accumulation of errors in the Ah count.

And my "Charged" parameters are programmable as well. My MPPT controller has it's own opinion of "fully charged" too. It's kind of like having two clocks -- you are never sure what time it really is! (cue the song by Chicago)
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Old 27-07-2018, 08:25   #6
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Re: Can windgen mess up Amp-hr count?

My MBK on My Magnum auto resets too, but I continue to charge at absorption voltage until Im fully charged which is usually a couple of hours past what the AH counter says is 100%.
As long as I continue the charge until really charged, it's astonishingly accurate, usually within 1% of what the Smart Gauge says.

If I Accepted when it said I Was fully charged, I'd be slowly walking down in charge day after day.
For some reason my Smart Gauge catches up about the time I'm fully charged too, although it will lag well behind in the charge cycle.

Seems no matter how many or how fancy the gadgets you have are, you still have to be what decides fully charged most of the time.

With Solar, almost always I can replace the AH used, but not get to 100% fully charged, come up just a few percent shy, but you do that cumulatively day after day, and that's not good
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Old 27-07-2018, 08:50   #7
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Re: Can windgen mess up Amp-hr count?

Thanks guys, the more I learn the less I seem to understand all this stuff .

Thanks Paul, Iíll figure out what my programmable setting are, and see if they actually match my batteries. My batteries are nothing special. I doubt if I changed the Peukert setting at all, leaving it at the generic ďwet cellĒ number. So very likely it is wrong.

Like you A64, my MPPT usually reaches float on sunny days. The victron controller uses an algorithm where it will sit in absorption till the batteries reach 2 amp @ 14.4 volts, then it drops to float voltage at 13.8v. This again is the generic ďwet cellĒ setting, which I hope is close to what I have. It seems to leave my batteries in good shape, but like you note, my solar controller is still charging the batteries long after the BVM is reading full.
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Old 27-07-2018, 09:02   #8
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Re: Can windgen mess up Amp-hr count?

Same thing happens on my home's grid tie system.
One big gust and a 700 aH LiFePo4 bank goes from 70% to 100%. What??


I just leave the wind gen shut down except for winter windstorms and let the Magnum keep things happy.
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Old 27-07-2018, 09:08   #9
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Re: Can windgen mess up Amp-hr count?

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Originally Posted by Mike OReilly View Post
Thanks guys, the more I learn the less I seem to understand all this stuff .>>>>>>>>

Mike,


I thought for sure you'd seen this already:


For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Also read this one:

Programming a Battery Monitor (by Maine Sail)

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

and his newer 'site

https://marinehowto.com/programming-a-battery-monitor/
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Old 27-07-2018, 09:48   #10
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Re: Can windgen mess up Amp-hr count?

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Originally Posted by Stu Jackson View Post
Mike,


I thought for sure you'd seen this already:


For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Also read this one:

Programming a Battery Monitor (by Maine Sail)

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

and his newer 'site

https://marinehowto.com/programming-a-battery-monitor/
Thanks Stu, I have read this stuff, but it was a while ago ó probably the last time I had a charging problem . Iíll re-read it all in detail again. But I donít think my situation is the same as the ďgotchaĒ issue. My counter does reach zero. And Iím not seeing any low voltage numbers over time either. Iím actually NOT having any problem with my batteries or my chargers. Itís just this weird behaviour with the meter that Iím trying to understand.

To recap: the issue is, my monitor often does the last dozen or so hours in one sudden leap. And even after it reaches zero, my MPPT continues to charge the batteries, which I assume means they arenít fully charged.

Iím sure the input data for my battery bank and Peukertís constant are not 100% correct. I am using the generic numbers b/c I donít know either. I pay little attention to the SOC percentage. But Iíd still think the meter should be able to accurately measure amps-out and amps-in, as Mainsailís article says they do.

This is what confounds me Ö the fact that it will jump to zero so suddenly. But maybe this is where the incorrect Peukert number comes in???

Anyway, thanks for the links. I will re-read again.
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Old 27-07-2018, 10:57   #11
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Re: Can windgen mess up Amp-hr count?

Quote:
Originally Posted by Mike OReilly View Post

In the morning we are usually down anywhere from 30 to 70 amp-hrs based on the hour counter on the BMV. But what often happens is that it will get down to around -20 amp-hrs, and then it will suddenly leap to zero.

Why?

I assume the BMV can accurately measure amps-out and amps-in. Why does it commonly jump to the zero mark like this?
Quote:
Originally Posted by Mike OReilly View Post
But I’d still think the meter should be able to accurately measure amps-out and amps-in, as Mainsail’s article says they do.

This is what confounds me … the fact that it will jump to zero so suddenly. But maybe this is where the incorrect Peukert number comes in???

Anyway, thanks for the links. I will re-read again.

Try reading the article again, why it does this is in there......


That section begins with:
"Avoid Using Auto-Sync or Auto-Reset"




Making Your Battery Monitor More Accurate




.
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Old 27-07-2018, 11:33   #12
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Re: Can windgen mess up Amp-hr count?

Mike

Unless programmed differently a battery monitor considers the bank full when it is accepting 2% of capacity. With a typical 450 AH bank that leaves 9AH on the table. So at 441AH the monitor will jump to full, while the solar continues charging.

On a boat with continuous loads - refrigeration and others - I question the logic of having a float charge on solar. Bulk/absorption can continue till the sun gets low without any ill effects. Of course if you are leaving the boat with loads reduced or turned off for a while float should be re-instated.

Curious what Mainesail says about this.
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Old 27-07-2018, 12:45   #13
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Re: Can windgen mess up Amp-hr count?

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Originally Posted by Mike OReilly View Post
My charing system consists of both wind and solar, each on separate controllers. I have a Victron battery monitor (BMV 602). The solar is on a 3-stage MPPT Victron controller. The wind is on a basic voltage regulated controller. Just cuts off at a certain voltage.

In the morning we are usually down anywhere from 30 to 70 amp-hrs based on the hour counter on the BMV. But what often happens is that it will get down to around -20 amp-hrs, and then it will suddenly leap to zero.

Why?

I assume the BMV can accurately measure amps-out and amps-in. Why does it commonly jump to the zero mark like this?

My speculation is that the highly variable input from the windgen is somehow not fully being accounted for, but I really don’t know.

BTW, I don’t actually believe my batteries are back to 100% when the counter reaches zero — at least not based on the behaviour of my MPPT which usually reaches float some time after the BMV reads 100%.
Wind generator output is highly variable. The batteries could be at an acceptance rate of 5 A when the wind kicks up, the wind generator starts putting out 10 A and the controller starts putting the brakes on. For this reason, I would set the wind generator absorption, just under the solar cut-off
Voltage, so the wind generator pumps in the Amps if the battery is hungry, but as it nears full charge the more stable solar does the top up. Then at night as the battery charge diminishes, the wind takes care of any significant deficiency, until the solar can kick in the next day, (assuming there is sun).

Basically, you are using wind for bulk and absorption and solar to top up, if it can.
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Old 27-07-2018, 16:38   #14
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Re: Can windgen mess up Amp-hr count?

Mike the 602 reads from 0% (dead flat) to 100% (fully charged)
You can set it up exactly how you 'wish' to understand it.
I had mine set up to read 'usable' capacity until I went to LiFePO4 batteries.
eg. If you have 400Ahr's of lead/acid batteries and wish to only ever use 50% of that amount, I suggest you set 100% to read the 400Ahr and then set 0% when you've used 200Ahr. Set battery capacity as 200Ahr.
Doing that avoids having to brain convert all the time that 50% really means 0% and something needs doing to 'fix the problem'. Turn something off, turn on charging of some sort!
Always charge well past 100% although it won't show on the Victron. (as a percentage ... it will on Ahr.)
Did you get the "quick install guide" with the unit?
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Old 27-07-2018, 21:33   #15
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Re: Can windgen mess up Amp-hr count?

Stu, thanks for the links to the post by Rich Stidger. But I must take issue with this from his post:

Rich wrote:
" The scenario for the Link 20 gotcha is this: The charging current has tapered down to about 13A with 20Ah still to go with the charging voltage at 14.4V. Now one of the refrigeration units turns on drawing 5A. This causes the battery charge current to drop below the 2% threshold . . . "

Now, the fact that another relatively small load comes onto the charger may *momentarily* drop it's output voltage and the battery charging current will momentarily drop accordingly, but after a few tenths of a second or less, charger output voltage should return to whatever it was just before the new load came on line (response time is dictated by design of the Link voltage regulator). Since the voltage does return to it's previous state, so will the battery charge current, and the Link should remain in acceptance mode until several minutes have passed in the "fully charged" condition. In short, the Link is pretty good about dealing with that sort of transient condition, and I think it actually uses a delay of a couple of minutes before switching to float voltage.

Doug
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